Download How to calculate standard deviation and t scores

Using your graphing calculator to
calculate mean, standard deviation, and the two sample t test
Note: You will not have to calculate standard deviation or calculate t scores on any quiz or exam
that I will give you.
Please feel free to use any short cuts you know. The below methods
work with a TI-83 plus calculator.
Calculating a mean from a list of values
1. Hit STAT key
2. At 1:Edit hit enter
3. Place your values in L1 by using enter button
4. You may make another list of values as L 2
5. Hit STAT again
6. Arrow to ClrList, Hit ENTER
7. Hit CLEAR
8. Hit 2nd then STAT key
9. Arrow over to MATH
10. Arrow down to 3:mean, hit ENTER
11. Hit 2nd #1 button
12. Hit “)”
13. Hit ENTER to get mean
Calculating the standard deviation (s.d.)
Method #1: Calculating s.d. for one list of values.
1. Place a list of values in the calculator under L1.
2. Hit 2nd STAT
3. Arrow over to MATH
4. Arrow down to stdDev, Hit enter
5. Hit 2nd #1 button
6. Hit “)”
7. Hit ENTER to get the s.d.
Method #2: Calculating (s) for a frequency distribution.
1. Add the data into your calculator. For L1 add the values and for L2 add the frequency
numbers (see example below for clarification).
2. Hit STAT
3. Arrow to CALC
4. At 1: 1-Var Stats hit ENTER
5. Hit 2nd #1 button
6. Hit “,” (comma)
7. Hit 2nd #2 button
8. Hit ENTER
Notice the (s) is Sx, the sample size is listed at the bottom under n =
Example of a frequency distribution for men’s heights
x
f
60
4
63
12
66
44
69
64
72
56
75
16
78
4
Calculating the (s) using the method above should give you Sx = 3.57 with a sample size of 200.
The mean is 69.3
Calculating the two sample t test
Note: Your calculator may not take the absolute value of the calculated value for t so if t is
negative just ignore the negative sign.
1.
2.
3.
4.
5.
Place two lists of values in the calculator under L1 and L2
Hit STAT button and arrow to TESTS
Arrow down to 4: 2-Samp TTest, Hit ENTER
Arrow down and choose for Pooled: Yes
Arrow down to Calculate and hit enter
Notice how d.f. is calculated for you. You then go to the t table to find the appropriate
comparison score.
Example
Let us consider plant biomass data where seven measurements from one geographical location
are 438, 421, 430, 413, 409, 428, 419 (ignore units), and six biomass data from a second location
are 442, 451, 428, 446, 459, and 437.
Do a t test as shown above and you should have t = 3.66 (Remember to ignore negative).
The sample size of L1 is 7 and for L2 it is 6 so d.f. = 7 + 6 -2 = 11 (notice calculator did this)
From the table the t critical value at d.f. = 11 is 2.20. Since 3.66 is higher than 2.20 then we can
conclude that the two means are not the same.